The present disclosure relates to a host system using sideband signals through PCIe cabling links to control power to PCIe I/O expansion drawer I/O modules.
Peripheral Component Interconnect Express (PCIe) is a serial expansion bus standard for connecting a computer to peripheral devices. The PCIe standard is well known as a PC backplane interface standard, and has gained popularity as a high-speed cabling interface using PCIe cable pairs. PCIe cable pairs, or PCIe cable links, couple host systems to PCIe expansion drawers that increase, or “expand” the amount of PCIe slots of the host system.
PCIe cable links support similar signals as the backplane version of the PCIe bus structure, which include 1) high-speed differential wire pairs to transfer data and 2) additional wires that support “sideband signals.” Sideband signals provide additional functionality to the PCIe interface but are not directly involved in PCIe data transfers. The sideband signals may include a reference clock signal, a cable present signal, a platform present signal, a cable power on signal, a sideband return signal, a 3.3 V power signal, etc.
Some of today's I/O expansion drawers have a dedicated, proprietary service network running over separate service cables between the host system and I/O expansion drawers to provide servicing functions such as concurrent maintenance. Concurrent maintenance allows an operator to perform maintenance on the system while a portion of the system is powered on. The host system includes a service processor that owns the service network connection to the I/O expansion drawers and sends commands over the separate service cables to control power to the I/O expansion drawers during drawer-level concurrent maintenance.